Aerial-traffic control



Get. 5 1926.

L. H. PETER AERIAL TRAFFIC CONTROL Filed March' 9, 1920 5 Sheets-Sheet 2HIS ATTORNEY aerial traiiic and has for its-object to vide systems ofand apparatus for signa ing Patented Oct. 5, 1926.

UNITED STATES PATENT corsica.

LESLIE BURST PETER, OF LONDON, ENGLAND, ASSIGNOR, BY MESN ASSIGNMENTS,

TO THE UNION SWITCH & SIGNAL COMPANY, F SWISSVALE, PENNSYLVANIA, A`

CORPORATION 0F PENNSYLVANIA.

AERIAL-Triennio oon'rnonj," f

Application led March 9, 1820, Serial No.

This invention relates to the control of of the special characterrequired by the development of aerial transport whereby `assists, fananieren Britain Apru asliaisgf a group" ofY landing land talringioiffl`lights indicated at4, 1 5, 6, 7, 8, 9, respectively. These 'lights areof the nature of Search 'z lights, lserving to'provide generalillumination for -thewcourse .takenl by aircraft arriv# greater securityand eiiieiency in the control -ing at or'ldeparting from 'theaerodr'omaand of incoming and outgoing aircraft from an aerodrome, depot or otherstation may be ensured.

According to the present invention signaling apparatus of suitablecharacter is pro-v vided at or adjacentto the aerodrome or depot, thecontrol of the signals being effected by a system of interlocking andindi'- eation, wherebyfconiiicting signals as regards aircraft 'arrivingor departing or as regards direction of wind cannotbe given: Theinvention also contemplates the 1nterlocking of the various signals withother controlling and indicating elements such as search lights andboundary lights in the case of aerial tralic during the hours of dark,-

ness.. A Theinvention isillustrated in panying drawings of which; Figure1 is a plan view *illustrating diagrammatically the generalarrangementofa system of night signaling at an aerodrome embodying theinvention. l 'l I AFigure 2 is a diagram of apparatus and connectionsillustrating one method o controlling t-he various signaling devicesillustrated in Figure 1. v y

Figure' is a diagrammatic view similar to Figure 1 but illustratin amodied signaling system, Figure 4 eing the corresponding diagram ofcontrol connections.

Figure 5 is a diagrammatic view similar to Figures 1 and 3 andillustrating a further modification, Figure 6 beingl a diagram ofcontrol connections for the system of Figure 5.

Fig. 7 is a view similar to Fig. 1 but showing the direction in whichthe lights 5 and 6 are trained when these lights are opi erative.

Referring nowto Figure 1 the aerodrome ground l is indicated assurrounded by a limiting boundary 2 defined so far as night signaling isconcerned by a ring of boundary lights indicated at 3.v At a number ofpoints on or adjacent lto the boundary 2 are central aircraft' 'ing traipaths 'Ton the aerodrome. The lights 4 to 9 inclusive are, are shown inFig. 1, arranged to be employed 'in' adjacent pairs, the right handlight looking along the beam being utilized for illuminating aircraftlanding at the'aerodrome'and the vleft hand light serving departingaircraft. The particular pair of the lights 4 to 9 inclusive which isoperative at any given time will in general be ldetermined in accordancewith the local lconditions and requirements and will more particularlybe dependent upon the direction of the prevailing Wind at the time in'order that both departing and arriving aircraft may be lable to face thedirection of The aerodrome is also provided withla'ndof which, namelythat indicated at 10 constitutes a danger signal, the other .signallight 1l indicating safety, Take oil or Iso theyfrnaygbv said'to belights for -indicatl Y i l60 departure signal lights indicated at 12, 13ref spectively are also provided, the signal light 12 being a dangersignal and signal light 13 l 'a' safety signal. A third pair of signallights indicated at 14, 15 are also provided hereinafter 'termedcircuit'lights, the signal lights 14, l'g'being differently colored .orotherwise rendered distinctive so as to indicate to arriving ordeparting aircraft whether a t rightl or vle'it hand circuit or curved"cours'e'fis to bey taken uppn arriving at or departin'gfrom theaerodrfome accord- 'ingto-whether the signal. light 14 or 15 is.operative. rlhese three'groups of lights will hereinafter begraferred'tobroadly as trafiic signals.

The aerdrbmeis l"finfuiei Ipieaaai with 1 'lighthouse 16 for indicatingthe i location' of distance therefrom.

In order to control the operatlon of the traiiic p-ath lights 4 to9.inclusive in laccord- Ithe aerodrome to aircraft/at a considerableance with the direction of the prevailing wind the apparatus indicateddiagrammati' cally in the upper right hand corner ot Figure 2 may beemployed. By reference to this ligure itwillbe seen that the circuitconductors 17 which supply operating current to the lights 4 to 9inclusive are conn nected to a ring main 18 'and to a rotatable contactsegment 19 respectively. The pairs of conductors indicated at 4c, 5c,6", 7, 8C, 9, supplying the lights 4 to 9 inclusive are connected to thering main 18 and to iixed contacts adapted to be engaged by the movableContact 19 as the latter rotates, 'and the contact 19 is arranged to beset into a position depending upon the direction of the prevailing windby means of any suitable meehanism such for example as a wind vane V.

Itwill be seen for instance that in the position shown in Figure 2 themovable contact 19 is in such a position to cause operatingcurrent to besupplied to the lights 4 and 5, aving been set into this position owingto the (prevailing wind being in the direction 1n icated by the arrow20. Operating current is thus supplied to the lights 4,5,

the remaining lights being inoperative Jfor this direction of wind.

As shown in Fig. 2, the control system for operating the various signallights of the aerodrome comprises a number ofindication relays 4f, 5f,6*, 7', 8f, 9', corresponding respectively to the lights 4 to 9inclusive. Each of the relays 4', to 9*, is arranged-to be energized.only when itscorresponding light is properly o erative 'and these relaysthus constitute in ication devices and effect by means of their movablearmatures the proper connections for automatically controlling theoperation of the signal lights of the aerodrome as will be hereinafterexplained. As here shown, each indication relay is included in series.with the corres nding signal light. The landing, take o and circuitsignal lights are also provided with corresponding relays indicatedat21, 22, 23 respectively which control, by means of their correspondingarmatures, the supply circuits for operating these signal lights. Theboundary lights 3 are also provided with an indication relay 3f which isincluded in circuit with these lights as illustrated. The control of thesignal lights is eii'ected by means of three control switches or leversindicated diagrammatieally at 24, 25, 26, the control switch 24corresponding to the circuit lights 14, 15, the control switch 25 to thetake off lights 12, 13 and the control switch 26 to the landing lights10, 11.

The control switches 24, 25, 26, are provided with automatic locksindicated at 27, 28, 29, respectively, adapted to be released by lockingmagnets 30, 31, 32, as shown in the figure, the construction of theselocking arrangements being such that the opening movement of the controlswitches is effected in two stages the latter of which cannot becompleted until the signal setting due to this movement has actuallytaken place, as cxplained hereinafter. V

The general operation oil the signal system shown in Figures 1 and 2will now be described.

The traiiic path lights 4 and 5 having been rendered operative by theaction of the automatic control mechanism indicated in Figure 2 inaccordance with the wind direction corresponding to that indicated-bythe arrow 20. the indication relays 4r and 5f are energized providedthat the lights 4 and 5 are. properly operative. The relay armatures 33`34, of the relay7 4f, and the armatures 36. 37, 38, 39, of the relay 5f.are consequently in their upper Ior attracted position.

Assuming that the boundary li Ylits 3 have also been rendered properlyoperative the indication relay 3r will be energized and its L armatures40.y 41, 42 will also be in their upper or attracted position. Thecontrol switch 24 is indicated as being in its open position andconsequently the circuit of the relay 23 is interrupted by the controlswitch 24 and this relay is de-energized. The armatures 43, 44 of therelay 23 are therefore in their lower or unattracted position with theresult that a circuit is completed from a positive terminal 45 of asource of electrical energy through the armature 43, the circuitsignalight 14 to the negative terminal 46. The signal light 14 is thusilluminated and a corresponding circuit direction is indicated foraircraft approaching or departing from the aerodrome. Owing to theposition ot the armature 44 a circuit is also completed from a positiveterminal 47 through the armature 44, conductor 48. the locking magnet 30of the control switch 24, to a negative terminal 49, so that magnet 30is energized. When the control switch 24 is moved to its closedposit-ion a circuit is completed from a positive terminal 50 through thecontrol switch 24, conductor 51, armature 42 of the llO indication relay3, conductor 52 and the relay winding 23, to a negative terminal 53. Therelay 23 being thus energized. its armatures 43 and 44 are moved totheir upper or attracted position with the result that the circuitbetween the terminals 45 and 46 includes the other circuit signal light15, the signal light 14, being rendered inoperative. Atthe same timeowing to the movement ot the armature 44 of the relay 23 the circuitthrough the locking magnet 30 of the control switch 24 is interruptedand the lock 27 is thus rendered operative. When it is desired torestore light 14 to its illuminated condition, the control switch isagain moved towards its open position, the lock 27 being arranged topermit sufficient movement of this switch to open the circuit of relay23. If this relay then actually opens, its contact 47 again closes thecireuittor magnet 30 so recipes that the switch may be moved to its fullopen position as shown in the drawing.

ln Figure 2 it will be seen that the control switches 25, 26 are both intheir closed position having been moved thereto to give permission totake ott and permission to land signal indications respectively. Thecircuits completed by the control switches 25, 26 are as follows: trom apositive terminal 83 through the control switch 25, conductor 5l,armature 4-1 ot the relay Sr, conductor 55, armature 34 ot the relayLlf,

armature 3S of relay 5r, conductors 56 and- 57 relay winding 2o tonegative terminal 58. The armatures 59, GO of this relay are thereforeheld in their upper or attracted position with the result that a circuitis com pleted from a positive terminal (il through the armature 59,conductor 62, signal light 13, to negative terminal. The signal light 13being thus rendered operative a permission to take olf indication isgiven. Owing to the fact that the armature is in its upper position itwill be noted that the circuit of the locking magnet 31 from a positiveterminal 64 thrdugh the conditetor 65, to the negative terminal 6G isinterrupted at the armature 60. The locking magnet 3l /is thusde-energized and the lock 28 ttor the control switch 25 is thereforerendered operative.

The circuit completed through the control switch 26 is from the positiveterminal 67, through the control switch 26, armature 40 ot relay 3T,conductor G8, armature 33 of relay 4F, armature 36 of relay 5f,conductor 69, relay winding 2l to the negative terminal 70. The relaywinding 21 being thus energized Aa circuit is completed from a positiveterminal 7l.v through the upper re-V lay armature 72 of the relay 2l,conductor 73, signal light ll, to a negative terminal 74. The signallight 11 being thus rendered operative a permission to land signalindication is given. It' will be noted that as in the case of thecontrol switch 25 the circuit ot the locking magnet 32 of the controlswitch 26 is interrupted at the lower armature of the relay 2l andconsequently when the control switch 2GI has been set into its closedposition the lock 29 becomes operative.

It will be readily understood that owing to the provision of the lockingdevices 27, 28, 29, for the control switches 24, 25, 26, the operationof these switches 24, 25, 26 is eliected on the well known indicationgsystem, that is, to say in opening any of the control switches theopening movement cannot be completed until the change in signalindication etlected .thereby has actually `occurred owing to the tactth'at the setting ot the signal it properly effected causes the lock tohe. released and thus aliords an indication to the operator that thedesired settingV has been obtained. For example, when it isdesired toextinguish the permission to take olif signal 13 and illuminate signal12, switch 25 is rst moved to- 'ards its open position, the lock 2Sbeing arrangei'l to permit sutiicient movement in this direction to'openthe. circuit of relay It this relay then actually opens, it closes thecircuit for lock magnet. Sl so that switch 25 is releasedaud may then bemoved to its full open position. The opening of switch 26 isaccomplished in similar manner.

As will be seen trom the circuits above described the energization ofthe relays 21, 22, 23 't'or enabling the corresponding signalindications to be given is dependent upon the indication relay 3 beingenergized, so that in the event ol any failure in operation of theboundary lights 8, the safety signal indications given will be cancelledand replaced by danger signal indications. Furthermore the energizationof the relays 21, 22 for giving permission to land and take ott isdependent upon the indication relays 4f, 5" being energized, so that inthe event of any failure in operation of the lights 4, 5 the permissionto land and take ott signal indications will be cancelled.

1t will be understood that the lights 4 to 9 inclusive and theircorresponding relays 'lvto 9T inclusive are arranged to be operated inadjacent pairs as above explained and the circuit through which therelay magnets 21 and 22 receive energizing current will be dependentupon the pair of indication relays fl tot)r inclusive which areoperative, at a given time. As shown in Fig. 2, ythe lights 4 and 5 areilluminated so that relays 4r and 5 are energized. rThe landing signalrelay 21, is lcontrolled by contact 33 ot relay 4f and contact 36 ofrelay 5r, so that if either ot the corresponding lamps should becomeextinguished the landing signal relay 2l would become cle-energized,whereupon the sate lamp 1l would be extinguished and Ithe dangerlamp l0become illuminated. The departure signal relay 22 is controlled bycontact 34 of relay e and contact`38 of relay 5*, so that it eitherlight 4 or 5 should become extinguished relay 22 would be de-energizedand so would extinguish the sate lamp 13 and illuminate the danger lampl2. l will now assume that owing to a change in wind direction light 4-becomes extinguished and light 6 becomes illuminated, no changeoccurring in the condition ot' light The landing signal relay 2l wouldthen be controlled by contact 37 ot relay 5r and Contact S2 ot relay 6r,while the departure signal relay 22 would then be controlled by Contact39 ot relay 5 and contact Sl ot relay 6r. The circuits which are thenellective for the re lays 2l and 22 will be obvious vfrom the drawing,andv consequently, they need not be traced in detail. lVhen, owing to afurther change in Wind direction the lights 6 and 7 will include contact95 of relay 8r and con-VV tact 96- 'of relay 9. .When lights 9 and 4,are operative, the circuit for the landing V signal rela becomeoperative, the landing signal 21 will be controlled by contact 85 ofrelay 6lr and contact 86 `of relay 7, while Ithe departure signal relay22 will then be controlled by contact 87 yoi relay 6r and contact 88 ofrelay 7'. Similarly, when lights 7 and 8 are operative, the landingsignal relay 21 will be controlled by contact 89 of relay 7' and contact90 of relayv 8f, while the departure signal relay 22'will be controlledby contact 91 of relay 7" and contact 92 of relay 8. When lights 8`and`-9 are operative, the circuit for the landingV relay 21 willinclude contact 93 of Irelay 8r and contact 94 of relay 9', While thecircuit for-the departure signal relay 22 21 will include contact 33 ofrelay 4, t e backv point of contact `36 of relay and contact 97 ot relay9"; while the4 circuit lfor the departure signal relay i 22 will includecontact 35 of relay 4r and contact 98 of relay 9T. In any instance, it'one or the other ot' the landing and take-oli L lights which are placedin operation should become extinguished, it will be apparent that bothof the signal relays 21 and 22 will become de-energized so that thelanding and departure signals will both indicate danger.

. The operation of the apparatus shown in Figs. l and 2 will now beapparent. Assuming that the control of the landing and takeofi lights 4to 9, inclusive, .is automatic, the

operator at the aerodrome can control only the landing signal lights,the take-oli signal lights and the circuit lights. As shown in thedrawing, circuit light 14-is illuminated, but in order to extinguishthislight and illuminate the circuit light 15, the operator merely reversesthe circuit. controller 24.*- To restore these lights tothe conditionsshown in the drawing, the operator returns 'circuit i controller 24towards. its original position, and if relay 23 responds by opening, it're-` I Vleases the lock 27 so thatv the returnmovement ci .circuitcontroller 24 maybe com pleted. The operation of circuit controllers 25and 26 for the control of the landing and' departure signal lightshasjbeen fully. ex-y plained hereinbefore. i. v f v It will beunderstond that-the direction in Iwhich each of the landing and take-offlights 4 to 9 is trained will depend upon Whether it is co-operatingWith'one or the other ofl the next adja'centlightgand this direction ortraining may' be arranged to be elected either manually` or byanysuitable mechaM nism. That i-s to say, the two lights which areilluminated atany one time will be so trained that their beams will bedirected transversely across the aerodrome ground 1 andY parallel withthe direction of the wind.

ranged to be moved so as to occupy various positions at or near' theboundary 2 of the aerodromc in accordance with the direction of the windor other conditions. The position of these lights may be controlled byany suitable means, such for example as by mechanism governed by a windvane V. The

-lights 4, 5 are each provided with indication relays 4r and 5r adaptedto be energized only when the lights 4, 5 are properly operative, theserelays being controlled in the same manner as the .corresponding relaysJ in Fig. 2. These `indication relays are arranged to control relays 21,22 for the landing signal lights 10, 11 and the taking off signal lights12, 13 respectively. The operation ot this system is very similar tothat of the system described with reference to Figures 1 and 2 except,as will be observed, the control switch 24 for the circuit lights 14, isnot shown as provided with any locking mechanism. An additional controlswitch indicated at 76 is provided for conchts 4, 5 areprovided, theselights being, thowever, arv

trolling the boundary lights 3, the circuit controlled by this switchbeing from a positive terminal 77, through the control switch 76,conductor 78, the indication relay 3f, to a negativeterminal 79. Therelay 3*' is in this system provided with armatures 40, 41

ture 80, conductor 82, through the boundary lights 3, to a nega-tiveterminal 83.

The locking arrangements for the control switches 25, 26 dili'er fromthose ofthe corresponding switches inithe system ,shown in Figures 1 and2 inasmuch as the circuit of the locking magnet 31for the taking offl ycontrol switch is controlled by the armature 75 of the relay 21forlanding signal lights. On the other hand the circuit of the lockingmagnet 32 for the control switch 26 is controlled by the armature of therelayy 22 for the taking off signal light. The armature when in itsattracted position is arranged to break theV circuit of the lockingmagnet 31 whereas the armature 60 when inv a similar position isarranged to complete the circuit of the locking magnet 32. As a resultof this arrangement although both `controlling the `circuits of therelays 21, 22 Y for the landing'and taking oi signal lights and with athird, armature'vSO which in its attracted position completes a circuitfrom a positive terminal 81, through relay armano'v y rennt/ee thecontrol switches 25 and 26 can be moved to their closed position thecontrol switch 26 cannot be reopened until the Control switch 25 hasbeen reopened. If the control switch 25 is 'open the control switch 26can be closed but cannot be reopened. These interlocking arrangements ofthe control switches are merely illustrated by way of example as showingone of a number oi different interlocking arrangements which may beadopted to meet particular conditions.

rlhe operation oi" the apparatus shown in Fig. 4, is as follows:

The control of the boundary lights 3 by the control switch 76 will beapparent from the circuits shown in the drawing; that is, when thecontrol switch 76 is closed, as shown, relay 3r is energized so that thelights 3 are illuminated. lf the operator desires to extinguish theselights he swings the control switch 7 6 to the open position, therebyde-energizing relay 3f, which in turn opens the circuit for the boundarylights at con.- tact S0. `When relay 3lr is de-energized, the circuitsfor the landing and departure signal relays 21 and 22 are opened atcontacts 40 and 41, respectively, so that the landing' and departuresignals will indicate danger, re gardless of any manipulation oi thecontrol switches 25 and 26. i The operation of the circuit lights 14 and15 will be apparent from the drawing; that is, when the control switch24 is closed relay 23 isenergized so that light 15 is illuminated. vWhenthe operator desires to reverse this signal he swings the control switch24 to the open position, thereby cle-energizing relay 23 which in turnextinguishes light 15 and illuminates light 14.

As shown in the drawing, the control switches 25 and 26 are both open,so that relays 21 and 22 are both open, and the land ing and departureindication signals both indicate danger; that is, thelights 10 and 12are illuminated. W'hen the operator desires to permit an aeroplane todepart from the field, he swings the control switch 25 to the closedposition, thereby energizing relay 22 and reversing the condition of thedeparture signal lights 12 and 13. Magnet 31 then remains energized, dueto the fact that contact 75 of' the landing signal relay 21 is closed,and hence the operator can at will return the control switch 25 to itsopen position wherein the departure signal will indicate danger.Similarly, if the operator desires to allow an aeroplane to land on thefield, heswings the control switch 26 to its closed position, therebyenergizing relay 21 and reversing the condition of the landing signallights 10 and 11. ln order to return the landing control switch 26 toits open position, however, the operator must rst close the departureswitch 25, thereby energizing relay 22. This operationicloses theextinguished the indication relay 5 will be deenergized, so that thesafe departure light 13 cannot be illuminated.

Referring now to Figures 5 and 6 a Somewhat more elaborate system ofsignaling is illustrated in which each of the landing and taking; oli'lights 4 to 9 inclusive is provided' with its own landing and takingoli' signal lights the signal lights for each of the lights 4 to 9inclusive being indicated at 4a, 5a, 6, 7', 8a, 9a, respectively, thecorresponding taking oli' signal lights being indicated at 4b, 5b, 6,7b, 8b, 9b, respectively. The landing and take-off lights 4 to 9,inclusive, are operated in adjacent pairs as in Fig. 1, and the pairwhich is operativeat any given time may be selected in the manner Setforth in explaining Fig. 1. rlhe control of the circuit lights 14 and,15is omitted from Fig.' 6 to simplify the drawing. rFhe indication relays3r to 9?, inclusive, are controlled b the boundary lights and by thelanding and take-oil lights through the medium of apparatus which may bethe same as that shown in Fig. l, but which is omitted from Fig. 6 t0simplify the disclosure.

As shown in Fig. 6, the boundary lights.

3 are illuminated and the landing and takeofi lights 4 and 5 .areoperative. rl`he control switches 25 and 26 are both closed, so that thelanding signal lights 4a are illuminated by virtue of a circuit whichpasses trom the positive terminal of a source of current through thecontrol switch 26, contact 40 of indication relay'3f, wires 99 and 100,contact 101 of relay 4, front point of contact 102 of relay 5f, wire 103and lights 4a to the negative terminal of the source of current. ylhetake-oli' lights 5b are illuminated by virtue of a circuit which passesfrom the positive terminal of the source of current through the controlswitch 25, con-4 tact 41 of relay 3V, wire 104, contact 105 of relay 4r,contact 106 of relay 5f, wire 107, and the lights 5b to the negativeterminal of the source ot' current. Assuming now that the landing andtake-olf lights 5 and'6 become operative, it is obvious that relay 4rwill open and relay 6t will close. The landing signal light 5 will thenbe illuminated by virtue of a circuit which passes from wire 99, throughwires 107 and 103, contact 109 of relay 5r and Contact 110 of relay 6r.

The take-off signal 6b Will be illuminated u through a circuit Whichpasses from posiy signal 8b is controlled by contact 122 of relay 7 andcontact 123.0f relay 8f. Landing signal 8a is controlled by contact 124.of relay 8f and contact 125 of relay 9', Whereas the 'take-ofi' signal9b is controlled by contact 101 of relay 4.', back point offcontact 102of relay 5lr and Contact 126 of relay 9'. The landing signal 9a and thetake-0E signal Ll" are connected in series, the circuitv being frompositive terminal 111', through Wire 112, Wire 127, signal 4b, contact128 of relay 4.', Wire 129, contact 130 of relay `9f,

Wire 131, and signal 9a to the negative ter' minal 132 of the samesource of current. These two last-mentioned signals will be illuminated,of course, only when indication relays 4f and 9r are energized, that is,only when the landing and take-off lightsfl and 9 are illuminated. Asexplained hereinbefore in discussing Figs. 1 and 2, the landing andtake-oli lights 4 to 9 are shifted in pairs so that the two lights whichare burning are directed across the aerodrome in directions parallel tothe Wind.

It Will be seen that the invention is of extremely wide scope and may beembodied in many different types of signaling systems, all howeverincluding the essential features of the invention, namely the'interlocking and indication of the setting of the signals, illuminatingand boundary or position indicating apparatus employed so as to preventconicting or otherwise dangerous signals being given.

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is 1. In combination, an aerodrome provided' with boundarylights, a circuit for said lights, signals for conveying information toaeroplanes'with res ect to the aerodrome, and means for control ing saidsignals partly by means associated With said boundary light circuit.

2. In combination, an aerodrome, means for defining the boundarythereof, a circuit .for said means, and landing and taking-olf signalscontrolled partly by means associated with said circuit.

3. In combination, an aerodrome, means for defining the boundarythereof, a signal for conveying information to aeroplanes with respectto the aerodrome, and includ- 7r Whereas the take-off signal 7b is con-1 ing means to indicate danger and safety, and means cont-rolled by saidfirst means for preventin saidsignal from indicating safety if saidunda-ry defining means is not in operation.

4. In combination, an aerodrome, means for defining the boundarythereof, a circuit for said means, trallic signals for conveyinginformation to aerop1anes, with respect to the aerodrome, and means forcontrolling said signals in part by said boundary dening means.

5. In combination, an aerodrome, means for indicating a traic paththereon, a traffic signal for'the guidance of aeroplane pilots and meansfor controlling said traffic signal comprising said first named means.

6. In combination, an aerodrome, means for indicating a traiic paththereon, means for indicating the boundary of. said .aerodrome, atralfic signal for the guidance of v 8. In combination, an aerodrome, aplurality of devices for indicating a tramo path thereon, means foroperating said devicesl i selectively a traffic signal for the guidanceof aeroplane pilots, and arranged to indi' cate danger and safety, andmeans for re venting said signal from indicatin sa ety if the particulardevice which is un er selec.

tion is not functioning.

9. In combination, an aerodrome, a plurality of devices for indicating atrafiic path thereon, means for operating said devices selectively anindication relay for each device, a traffic signal, and means forcontrolling said signal b said relays.

10. In com ination, an aerodrome, means for indicating a traffic paththereon, a trafiicv signal for conveying information to aeroplanes withrespect to, said aerodrome and controlled by said means, and manuallyoperable ap aratus for the further -control of said signa 11. Incombination, an aerodrome, means for defining the boundary thereof,means for indicating a traffic path on said aerodrome, a, traffic signalfor conveying information to aeroplanes with respect to said aerodromeand controlled by both of said means, and manually operable means forthe further control of said signal.

12. In combination, an aerodrome, devices located at intervals aroundthe boundary thereof, means for operating said devices in pairs toindicate trafhc paths on means for preventing said signals. vom'm.-

devcesis in operation. f.

13. In eombnation,l angaerdromela, plu# ralit of traffic path indicatingdevlces 1o.- cate 4at intervals aru'nd lthe|` boundary tne'peratvecondition of the devi-ce, a trafc's al havin means to'ndcate safety andger, an meanseontrolled by `5re1ays 4for preventing ,sa-id signal from111-. 1 dcatjngksafety un1essapair vf." adjacent devices is;Ainoperative condition.'

1 In ,tf astlnmiy,s vherenflr ,my signatheveof, means'for operting saiddevices in' j lo pairs, n relay for escl delvxce respon'selto fY DESIJE'PETER.

